Photoelectric smoke detector

ABSTRACT

A photoelectric smoke detector comprising a source of light intermittently energized to flash by the output of a first oscillator, and a light receiving circuit energized and operated intermittently by the output of a second oscillator, wherein the oscillation periods of the first and second oscillators are different from each other, and the outputs of the first and second oscillators are applied to the light source through an AND gate, whereby the light receiving circuit is brought into operation when a light is emitted from the light source.

United States Patent 191 Kawakami PHOTOELECTRIC SMOKE DETECTOR [75]Inventor: Mamoru Kawakami,Takatsuki,

Japan [73] Assignee: Hochiki Kabushiki Kaisha, Tokyo,

Japan [22] Filed: Dec. 10, 1973 [21] Appl. No.: 423,530

[30] Foreign Application Priority Data June 3, 1975 11/1972 Koning250/209 X 4/1974 Bossons 250/214 R Primary Examiner-Walter StolweinAttorney, Agent, or FirmWaters, Schwartz & Nissen [57] ABSTRACT Aphotoelectric smoke detector comprising a source of light intermittentlyenergized to flash by the output of a first oscillator, and a lightreceiving circuit energized and operated intermittently by the output ofa second oscillator, wherein the oscillation periods of the first andsecond oscillators are different from each other, and the outputs of thefirst and second oscillators are applied to the light source through anAND gate, whereby the light receiving circuit is brought into operationwhen a light is emitted from the light source.

[56] References Cited UNITED STATES PATENTS 3 Claims, 4 Drawing Figures3,655,289 4/1972 Walker 250/206 X 1' 1 i r l i 1 OSCILLATOR P-q PULSEAMPLIFIER LIGHT souncs I OSClLLATOR PULSE AMPLlFlER 5 AMPLIFIER ALARMSIGNAL CIRCUIT LIGHT RECEIVER /4 I L'TI IIIur-m I975 3.887.815 SHEET IFIG. I PRIOR ART I S oscILLAToR PuLsE AMPLIFIER LIGHT souRcE I I I ALARMSIGNAL cIRcuIT AMPLIFIER LIGHT REcEIvER oscILLAToR PuLsE AMPLIFIER FIG.2

1 I I I I oscILLAToR PULSE AMPLIFIER LIGHT souRcE I I 1 oscILLAToR PuLsEAMPLIFIER LIGHT REcEIvER f4 5 I AMPLIFIER I ALARM sIGHAL cIRcuITPHOTOELECTRIC SMOKE DETECTOR FIELD OF THE INVENTION This inventionrelates to photoelectric smoke detectors.

BACKGROUND OF THE INVENTION Photoelectric smoke detectors are known inthe art in which in order to realize a reduced power consumption, alight source operating circuit and a light receiving circuit areperiodically energized in synchronism with each other so that the lightsource is intermittently operated and the light receiving circuitreceives the flashes of light scattered by smoke. A disadvantage of thistype of detector is that it is technically difficult to achieve therequired synchronization of the light source operating circuit and thelight receiving circuit due to the fact that the time constants of thecomponent elements of the one circuit are not the same as those of thecomponent elements of the other circuit and moreover a considerable timeis required for pro viding the required synchronization both in thedesigning and manufacture of such detector.

In an attempt to overcome the foregoing difficulty, a photoelectricsmoke detector has been proposed in Japanese Patent Application No.80l39/l97l, in which the light source and the light receiving circuitare intermittently energized by the outputs of their own oscillators,and oscillation periods of the two oscillators are selected to differfrom each other, whereby each time the light source andd the lightreceiving circuit come into operation simultaneously after a givennumber of cycles, detection of the presence of smoke is effected.

SUMMARY OF THE INVENTION It is an object of the present invention toprovide an intermittent energization type photoelectric smoke detectorwhich eliminates the need for synchronized operation of the oscillators,insures simplified designing and adjustments and reduces the amount ofpower consumption still further.

In accordance with the present invention, there is thus provided aphotoelectric smoke detector comprising a light source intermittentlyenergized by the output of a first oscillator, a light receiving circuitadapted to rereceive light from the light source and energized by theoutput of a second oscillator to operate intermittently, the oscillationperiod of the first oscillator being different from that of the secondoscillator, and an AND gate circuit connected between the firstoscillator and the light source and controlled by the outputs of thefirst and second oscillators, whereby the light source is operated onlywhen the outputs of the first and second oscillators operating with thedifferent oscillation periods appear simultaneously, thereby toeliminate any wasteful operation of the light source and thus to reducethe amount of power consumption still further.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is a block diagram of a priorart photoelectric smoke detector;

FIG. 3 is a pulse waveform diagram useful for explaining the operationof the device shown in FIG. 1;

FIG. 2 is a block diagram showing an embodiment of a photoelectric smokedetector according to the present invention; and

FIG. 4 is a pulse waveform diagram useful for explaining the operationof the embodiment shown in FIG. 2.

DETAILED DESCRIPTION FIG. I of the accompanying drawing is a blockdiagram showing the general construction of the photoelectric smokedetector disclosed in Japanese Patent Application No. l39/l97 I. In thisdevice, the output oscillations or rectangular pulses from an oscillatorI are amplified by a pulse amplifier 2 and, a light source or lamp 3 isenergized by the amplified output of the amplifier 2. The light source 3then flashes so that when the flashes of light from the light source 3are scattered by smoke, part of the scattered flashes of light isreceived by a light receiver 4 which in turn detects the presence of thesmoke. The output of the light receiver 4 is applied, afteramplification by an amplifier 5, to an alarm signal circuit 6 to give analarm. In this case, the light receiver and the amplifier do not operateat all times, but they are energized and operated intermittently by therectangular pulses generated by an oscillator 8 and then amplified by anamplifier 7. The alarm signal generating operation of this device willbe described further with reference to FIG. 3.

Referring to FIG. 3, numeral 11 designates the waveform of the pulsevoltage for energizing the light source 3, and numeral 12 designates thewaveform of the pulse voltage for energizing and operating the lightreceiver 4 and the amplifier 5. At times l r r r, and r,,,, the flashingoperation of the light source 3 and the operation of the light receiver4 and its associated circuits coincide with each other thus permittingthe performance of smoke detecting operations. At other times, eitherthe light source 3 or the light receiver 4 or both of them areinoperative and hence no smoke detecting operation is performed. Ofcourse, the repetition frequencies of these pulses are selected to belarge and therefore the performance of the smoke detecting operation atthe times r I I,, r I and r means that the occurrence of smoke can bealmost simultaneously detected and that the operation of this device asa smoke detector is satisfactory. However, at times t t and so on thelight source 3 is operated wastefully. Therefore, while this prior artdevice has the advantages of the considerably reduced power consumptionand simplified designing and adjustment due to the fact that there is noneed to synchronize the two oscillators, there still exists room forfurther reduction of power consumption since the light source and thelight receiver are separately operated wastefully excepting at thosetimes when both of them come into operation simultaneously. Since theamount of power consumed by this type of light source is generallyconsiderably large, it is possible to realize a further reduction in thepower consumption of the whole device by eliminating such wastefuloperation of the light source.

Referring now more specifically to FIG. 2 of the drawings, there isillustrated a block diagram of a photoelectric smoke detector whichembodies the present invention and which overcomes the foregoingdeficiencies of the prior art devices. In FIG. 2, the same referencenumerals are employed for the component parts which are similar to thoseused in the device of FIG. I. Numeral 9 designates an AND gate circuitwhich receives as its inputs the outputs of pulse amplifiers 2 and 7.Symbols A and B designate respectively a light source operating circuitand a light receiving circuit of the smoke detector. The light sourceoperating circuit A comprises the first oscillator 1, pulse amplifier 2for amplifying the output of the first oscillator l. and light source 3intermittently operated by the output of the pulse amplifier 2 andcomprising for example a light emitting diode or lamp. The lightreceiving circuit B comprises the light receiver 4 having aphotoelectric conversion element such as a photoelectric cell or phototransistor to receive the flashes of light emitted from the light source3 and scattered by smoke. amplitier 5 for amplifying the output of thelight receiver 4, alarm signal circuit 6 responsive to the output of theamplifier 5 to generate a detected smoke signal, and the secondoscillator 8 and amplifier 7 for periodically and intermittentlyenergizing the component parts 4 through 6. The oscillation periods ofthe first and second oscillators l and 2 are selected to differ fromeach other and each of them comprises for example a blocking oscillatoror astable multivibrator. For instance, as shown in FIG. 4. theoscillator l generates pulse output ll having an on-time 1 and anoff-time tr 4 1,,..). and the oscillator 8 generates pulse output 12having an on-time T and an off-time T (T,,,, T z 6.5 t

The operation of the embodiment shown in FIG. 2 will be described withreference to FIG. 4. The oscillators l and 8 oscillate independently ofeach other at different frequencies so that the oscillaor l generatespulses 11 having a narrower time width and the oscillator 8 generatespulses l2 having a wider time width. These pulses 11 and 12 arerespectively amplified by the amplifiers 2 and 7 after which the pulses12 are directly applied to the light receiver 4 and the amplifier tooperate them for a length oftime corresponding to the time width of eachpulse 12. On the other hand. the light source 3 receives the outputs ofthe oscillators l and 8 through the AND gate circuit 9 so that the lightsource 3 flashes only at times l i t I, and r Since the light receivingsection is invariably in operation at these times. the smoke detectingoperation is invariably carried out each time the light source 3flashes. In the case of the prior art device, as indicated by dottedlines. the light source 3 flashes at times I I... and so on when thelight receiving section is inoperative and therefore these flashes areall wasted. The device according to the present invention eliminatessuch wasteful flashes of the light source. thereby ensuring a longerlife of the light source and a further decrease in the powerconsumption.

It will thus be seen from the foregoing description that the deviceaccording to the present invention not only eliminates the need tosynchronize the effective operating times of the light source operatingcircuit and the light receiving circuit with the resultant eliminationof the required labor and special parts for the adjustment therefor. butalso minimizes the amount of power consumption due to the absence of anywasteful operation of the light source.

What we claim:

1. A photoelectric smoke detector comprising a source of light, a firstoscillator connected to said source, said source being adapted for beingintermittently energized by the output of said first oscillator, insecond oscillator. a light receiving circuit including a photoelectricmeans adapted for being energized by the output of a second oscillatorthereby to come into operation intermittently for receiving lightscattered by smoke generated by the source of light. the first andsecond oscillators having different oscillation periods, and an AND gatecircuit controlled by the outputs of the first and second oscillatorsbeing connected between the first oscillator and the source of light.

2. A photoelectric smoke detector according to claim 1. wherein theoscillation period of the first oscillator is shorter than theoscillation period of the second oscillator.

3. A photoelectric smoke detector according to claim 1. wherein thepulse width of the second oscillator is wider than the pulse width ofthe first oscillator.

1. A photoelectric smoke detector comprising a source of light, a firstoscillator connected to said source, said source being adapted for beingintermittently energized by the output of said first oscillator, asecond oscillator, a light receiving circuit including a photoelectricmeans adapted for being energized by the output of a second oscillatorthereby to come into operation intermittently for receiving lightscattered by smoke generated by the source of light, the first andsecond oscillators having different oscillation periods, and an AND gatecircuit controlled by the outputs of the first and second oscillatorsbeing connected between the first oscillator and the source of light. 1.A photoelectric smoke detector comprising a source of light, a firstoscillator connected to said source, said source being adapted for beingintermittently energized by the output of said first oscillator, asecond oscillator, a light receiving circuit including a photoelectricmeans adapted for being energized by the output of a second oscillatorthereby to come into operation intermittently for receiving lightscattered by smoke generated by the source of light, the first andsecond oscillators having different oscillation periods, and an AND gatecircuit controlled by the outputs of the first and second oscillatorsbeing connected between the first oscillator and the source of light. 2.A photoelectric smoke detector according to claim 1, wherein theoscillation period of the first oscIllator is shorter than theoscillation period of the second oscillator.